Wireless or mobile (cellular) communications networks in which a mobile terminal (UE, such as a mobile handset) communicates via a radio link to a network of base stations or other wireless access points connected to a telecommunications network, have undergone rapid development through a number of generations. The initial deployment of systems using analogue signalling has been superseded by Second Generation (2G) digital systems such as Global System for Mobile communications (GSM), which typically use a radio access technology known as GSM Enhanced Data rates for GSM Evolution Radio Access Network (GERAN), combined with an improved core network.
Second generation systems have themselves been largely replaced by or augmented by Third Generation (3G) digital systems such as the Universal Mobile Telecommunications System (UMTS), which uses a Universal Terrestrial Radio Access Network (UTRAN) radio access technology and a similar core network to GSM. UMTS is specified in standards produced by 3GPP. Third generation standards provide for a greater throughput of data than is provided by second generation systems. This trend is continued with the move towards Fourth Generation (4G) systems and Fifth Generation (5G) systems.
3GPP design, specify and standardise technologies for mobile wireless communications networks. Specifically, 3GPP produces a series of Technical Reports (TR) and Technical Specifications (TS) that define 3GPP technologies. The focus of 3GPP is currently the specification of standards beyond 3G, and in particular on standard for the Evolved Packet Core and the enhanced radio access network called “E-UTRAN”. The E-UTRAN uses the LTE radio technology, which offers potentially greater capacity and additional features compared with previous standards. Despite LTE strictly referring only to the air interface, LTE is commonly used to refer to the whole system including EPC and E-UTRAN. LTE is used in this sense in the remainder of this specification, including when referring to LTE enhancements, such as LTE Advanced. LTE is an evolution of UMTS and shares certain high level components and protocols with UMTS. LTE Advanced offers still higher data rates compared to LTE and is defined by 3GPP standards releases from 3GPP Release 10 up to and including 3GPP Release 12. LTE Advanced is considered to be a 4G mobile communication system by the International Telecommunication Union (ITU).
It is anticipated that 5G mobile communications systems will be rolled-out in the future. Currently, the network structure and wireless access interface to be used in 5G systems has not been decided upon. However, in order to reduce deployment costs and integrate with 4G systems, it is envisaged that 5G systems may utilise some of network architecture currently used in 4G systems.
Consequently, although particular embodiments of the present invention may be implemented within an LTE mobile network, they are not so limited and may be considered to be applicable to many types of wireless communication networks, including future 5G systems. However, due to the greater certainty surrounding the structure of systems based upon LTE network, embodiments of the present invention will predominantly be described with reference to the structure and network elements of LTE based systems. Consequently, an example LTE system is shown in FIG. 1.
The LTE system of FIG. 1 comprises three high level components: at least one UE 102, the E-UTRAN 104 and the EPC 106. The EPC 106, or core network as it may also be known, communicates with Packet Data Networks (PDNs) and servers 108 in the outside world, such as those which form the Internet for example. FIG. 1 shows the key component parts of the EPC 106. It will be appreciated that FIG. 1 is a simplification and a typical implementation of LTE will include further components. In FIG. 1 interfaces between different parts of the LTE system are shown. The double ended arrow indicates the air interface between the UE 102 and the E-UTRAN 104. For the remaining interfaces user data is represented by solid lines and signalling is represented by dashed lines.
The E-UTRAN 104, or radio access network (RAN) as it may also be known, comprises a single type of component: an eNB (E-UTRAN Node B) which is responsible for handling radio communications between the UE 102 and the EPC 106 across the air or wireless access interface. An eNB controls UEs 102 in one or more cell. LTE is a cellular system in which the eNBs provide coverage over one or more cells. Typically there is a plurality of eNBs within an LTE system. In general, a UE operating in accordance with LTE communicates with one eNB through one cell at a time, where an eNB may also be referred to as a mobile base station.
Key components of the EPC 106 are shown in FIG. 1. It will be appreciated that in an LTE network there may be more than one of each component according to the number of UEs 102, the geographical area of the network and the volume of data to be transported across the network. Data traffic is passed between each eNB and a corresponding Serving Gateway (S-GW) 110 which routes data between the eNB and a PDN Gateway (P-GW) 112. The P-GW 112 is responsible for connecting a UE to one or more servers or PDNs 108 in the outside world. The Mobility Management Entity (MME) 114 controls the high-level operation of the UE 102 through signalling messages exchanged with the UE 102 through the E-UTRAN 104. Each UE is registered with a single MME. There is no direct signalling pathway between the MME 114 and the UE 102 (communication with the UE 102 being across the air interface via the E-UTRAN 104). Signalling messages between the MME 114 and the UE 102 comprise EPS Session Management (ESM) protocol messages controlling the flow of data from the UE to the outside world and EPS Mobility Management (EMM) protocol messages controlling the rerouting of signalling and data flows when the UE 102 moves between eNBs within the E-UTRAN. The MME 114 exchanges signalling traffic with the S-GW 110 to assist with routing data traffic. The MME 114 also communicates with a Home Subscriber Server (HSS) 116 which stores information about users registered with the network.
In additional to the architectural structure discussed above, LTE also includes the concept of bearers, and in particular, EPS bearers, where data transmitted from and received by a UE is associated with a particular bearer. EPS bearers themselves may be formed from an e-Radio Access Bearer (e-RAB) which extends between the UE and EPC and S5/S8 Bearers which extend within the EPC. EPS bearers define how UE data is handled as it passes through the LTE network and may be viewed as a virtual data pipe extending through the core network, where a bearer may have quality of service associated with it, such as a guaranteed bitrate for example. A bearer serves to channel packet data to a Packet Data Network (PDN, also referred to as a Public Data Network) outside of the LTE network via the S-GW and P-GW, where a further external non-LTE bearer may be required to channel data from the EPC to an external network. Each bearer is therefore associated with a certain PDN and all data associated with the bearer passes through a particular P-GW. Each bearer is also identified by a Logical Channel ID (LCID) at the Medium Access Control (MAC) level, where one bearer corresponds to one logical channel.
The data packets transmitted over a particular bearer are also associated with a particular IP flow, where a bearer may have a plurality of associated IP flows. The IP flows associated with a bearer relate to a set of data packets that are exchanged between two nodes, for example, a UE and a video streaming server, which each have an associated IP address.
In the current 3GPP networks, it is assumed that each E-RAB/EPS bearer is handled by one P-GW. This P-GW will allocate the IP address to the UE (to be used for this and potentially other EPS bearers belonging to the same APN) when the UE first connects to the mobile operator network and establishes a data packet pathway from the P-GW to the UE. All packets destined to the UE for this APN will arrive into the operator network via the P-GW, where the P-GW may also be referred to as the IP anchor since the P-GW is the first/last point in the mobile operator network that all packets associated with a particular bearer/UE IP address must pass when being communicated to/from the associated PDN. In particular, routers in the PDN will be configured to route packets with a destination IP address of the UE to a single P-GW. The P-GW tunnels the packets to the S-GW using IP tunnelling, and the S-GW will subsequently tunnel the packets to the eNB to which the UE is connected. The tunnelling may be achieved via the use of IP encapsulation for example, where a packet entering having a destination IP address of the UE may be encapsulated with a new IP address of an intermediate router such as the S-GW. Once the encapsulated packet is received by the intermediate router, the router removes the encapsulation and associated IP address and routes the IP packet based on its destination address i.e. the address of the UE, where this routing may also be based on IP tunnelling. This process and network structure is illustrated in FIG. 2
The network of FIG. 2 has a similar architecture to that of FIG. 1, however, multiple P-GWs 212, 214, 216 and eNBs 204, 206, 208 are shown and the operator network is shown to include one or more routers 202 which assist in routing data packets to and from the appropriate eNB, S-GW and P-GWs, where the links between each individual router are also shown. Packets destined to the UE 200 (e.g. with IPaddr1) will arrive at the operator network via P-GW1 212. At P-GW1 212 the packets will be tunnelled in tunnel1 218 to the S-GW1 210 using IPaddr2 of the S-GW1 as destination address of the tunnel1 218 i.e. packets will be encapsulated using the IP address IPaddr2. Next the S-GW1 210 will remove the IPaddr2 encapsulation and tunnel the packets in tunnel2 220 with destination IPaddr3 of the eNB1 204 in order to deliver the packets to the appropriate eNB. Once received by the eNB1 204, the tunnelling is ended and the packets are transmitted to the UE 200 based on their destination address i.e. IPaddr1.
The routers 202, or switches or network equipment as they may also be known, of the network of FIG. 2 will know how to route IP packets to their IP destination address based on distributed routing protocols. Such protocols may for example include Open Shortest Path First (OSPF) in which routing information is exchanged between routers in order to fill/update a routing table/flow table of each router.
Although only one PDN connection is shown in FIG. 2, in practice a UE may have established many bearers, associated with one or more different PDNs. Therefore a UE may have many connections each of which go through a different P-GW and thus have different tunnelling routes and different IP anchors for each bearer. Furthermore, although also not shown, between the P-GWs and the Internet, there may be one or more routers supporting inter-domain routing protocols such as the Border Gateway Protocol (BGP) and the IP network may be operated by an operator different to that of the mobile network.
FIG. 3 illustrates a network with an equivalent architecture to FIG. 2, however, the UE 200 has moved and is now connected to eNB3 208. Consequently, tunnel2 220 has been altered since it is now tunnels IP packets to eNB3 208 which has IPaddr4 whilst tunnel1 218 remains unchanged since the S-GW and the P-GW of the UE's bearer have not changed. Therefore in the architecture of FIGS. 2 and 3, packets for an bearer enter the operator network via the same P-GW and packets are tunnelled from the P-GW to the appropriate eNB via a S-GW and two IP tunnels 218 220.
By virtue of maintaining a static S-GW and P-GW and using tunnelling, if a UE moves between eNBs, for downlink traffic, only the destination address of the second tunnel 220 is required to be updated (e.g. from eNB1 to eNB3), and there is no need to update any IP-level routing tables in routers. Furthermore, because the IP packets for the UE are tunnelled, the IP address of the UE (IPaddr1) is not used for routing at the network layer and may also remain unchanged. Consequently, the architecture of FIGS. 2 and 3 provide simple routing in which only the destination IP addresses of one or more tunnels is required to be changed.
However, a number of disadvantages may also result from the network architecture of FIGS. 2 and 3. Firstly, when the UE moves to a different part of the network (e.g. different side of the country), the same P-GW will remain in the route between the UE and the Internet or other external network if the UE's IP address is to be preserved. Therefore, it is not possible to change the P-GW of a bearer of a UE whilst preserving the UE's IP address since that P-GW is where all IP packets associated with the bearer (UE IP address) will be routed to by routers in the Internet or other external network. Conversely, if a P-GW is to be changed, the UE IP address will be changed and the connection with the PDN via the previous P-GW may be lost.